1. Field of the Invention
The present invention relates to apparatus and method for supplying a release coating to a fixing roller or similar device such as those commonly found in printers and copiers.
2. Description of Related Art
A typical laser printer or plain paper copier contains a series of rollers used to fix toner in place once it has been transferred to paper. Generally two rollers are arranged in contact with one another and rotating in opposite directions--a heated fixing roller and a resilient pressing roller. Once toner has been transferred to a sheet of paper, the paper is passed between the two rollers and toner is heat sealed in place.
In order to assure that the paper does not stick to the heated fixing roller during this procedure, a wick containing a release agent is mounted in contact with the roller along its length. A traditional wick has usually comprised a fibrous strip, such as one comprising "NOMEX.RTM." fiber sold by E. I. duPont de Nemours and Company, Wilmington, Del. These felts can be acquired from conventional industrial fabric suppliers such as Tex Tech Industries of North Monmouth, Me. The felt is presaturated with a release agent of silicone oil (e.g. dimethyl polysiloxane). In addition to assuring separation of the paper and fixing roller during the printing process, the wick also serves as a wiper to clean contaminants, such as residual paper dust, paper additives (e.g. clay, pigments) and offset toner, from the hot fixing roller.
While traditional felt/oil wicks enjoy widespread use due in part to their simplicity and relatively low cost, they are plagued with a number of problems. First, oil impregnated felt tends to provide inconsistent oil release, releasing excess quantities of oil upon initial installation and steadily diminishing to inadequate oil release over time. Second, felt tends to become clogged and caked with toner residue. Residue build up leads to: diminished ability of the felt to deliver oil; reduced effectiveness at cleaning the roller; and increased friction and wear upon the roller. Unfortunately, once contaminated, the matted surface of the felt makes it impractical to clean and requires its disposal. Third, the inability to clean the felt surface also makes it infeasible to attempt to regenerate the wick for reuse, leading to disposal problems and needless waste.
In recognition of some of these problems, a number of modifications to the basic wick design have been proposed. As is explained below, none is believed fully satisfactory.
In U.S. Pat. No. 4,668,537, issued May 26, 1987, to Matsuyama et al. it is proposed to adhere a strip of porous polymer membrane to a felt wick. While this addresses some of the problems inherent with use of a felt wick alone, there are a number of anticipated impediments with this approach. First, proper adhesion of a polymer membrane to a felt surface can be difficult to achieve and delamination in use is a distinct risk. Second, like use of a felt material alone, this device provides only a single contact surface against the fixing roller, which may be subject to premature wear and contamination. Third, the open nature of this device limits the amount of oil which can be loaded into the wick without leakage or clogging around the edge of the porous polymer strip.
Some of these concerns are addressed in U.S. Pat. No. 4,359,963, issued Nov. 23, 1982, to Saito et al. This patent teaches use of a elongated, relatively shallow bag of porous polymer, such as polytetrafluoroethylene (PTFE), filled with heat-resistant felt having silicone oil absorbed therein. Despite improved containment of the oil within the felt, most embodiments of this device continue to be problem prone, including: still supplying only a single contact surface between the wick and the fixing roller; requiring a somewhat difficult attachment of the polymer bag to a mounting frame; and presenting a risk of catastrophic oil leakage if the oil filled bag breaks. Another embodiment taught in this patent proposes use of a rotating polymer-covered felt wick. This approach may provide a better seal of the liquid within the felt, but the rotating movement of the wick against the fixing roller is believed to be less effective at cleaning the fixing roller surface and delivering oil onto the roller surface.
U.S. Pat. No. 4,375,201, issued Mar. 1, 1983, to Kato, employs a hollow tube of extruded porous PTFE which is filled with silicone oil and sealed or covered at both ends to prevent leakage. A coating of fluorocarbon rubber or other material is used to seal the pores in the PTFE tube in those areas not in contact with the fixing roller. While this applicator may address some of the problems of a felt and oil wick, as is discussed below it has a number of other deficiencies.
First, the use of a hollow tube containing a free-flowing reservoir of oil is unacceptable in many instances. For instance, the presence of a liquid reservoir means that the applicator must be kept level in order to have an even distribution of oil across the fixing roller. Additionally, the presence of oil in a free-flowing form presents a risk of leakage and damage to the equipment. To address the leakage problem, the patent teaches the use of sealing mechanisms on either end of the tube; however, such sealing mechanisms still present a risk of leakage and also add unnecessary bulk to the apparatus. Finally, with the loss of oil from the tube in the operation of the wick, undesirable distortion or collapse of the tube is possible.
Second, without the stability of a firm mass of felt or other material in contact with the roller, a hollow, tubular wick is believed to be less efficient at cleaning the roller than conventional felt-based wicks.
Third, the design of the apparatus of U.S. Pat. No. 4,375,201, is believed to add little in the way of increased operational life to the apparatus. Although the device appears capable of refill, this procedure may be far too cumbersome and prone to leakage for widespread acceptance. This conclusion is bolstered by the patent's suggestion that the device may be disposed of after use. Further, in order to avoid leakage, the pores of the applicator are intentionally sealed around most of its periphery to provide only a single roller contact surface. This allows the applicator to be used only so long as this single surface area can be maintained free from wear and residue build-up.
Similar devices are disclosed in U.S. Pat. Nos. 4,573,428, issued Mar. 4, 1986, to Ogino et al. and 4,631,798, issued Dec. 30, 1986, to Ogino et al. Both of these devices employ sealed porous polymer tubes filled with a free-flowing liquid release agent. As such, each is believed to suffer from deficiencies similar to those discussed above. Further, the use of a polyethylene in U.S. Pat. No. 4,573,428, is believed to have a number of additional problems, such as uneven pore structure, increased risk of clogged pores, and possible contamination of heated fixing rollers.
A more complex wick apparatus is disclosed in U.S. Pat. No. 4,459,625, issued Jul. 10, 1984, to Sakane et al. This apparatus provides an open reservoir of release agent which can be repeatedly refilled. Unfortunately, this applicator continues to have only a single contact surface while being substantially bulkier than any of the previously referenced devices. Additionally, the use of free-flowing liquid also presents serious leakage and operational limitations. Finally, this device requires relatively complex assembly techniques in order to create an adequate seal between the roller surface contact and the oil reservoir.
Another problem that has emerged more recently centers around the demand for small, portable high-quality printers and copiers. The particular demands in storage and use inherent in the portable market eliminates use of any release coating applicator which must be maintained in an upright, much less level position. Additionally, the size and weight demands for such equipment requires that the device used be as light, compact and durable as possible.
All of these concerns are addressed by the apparatus disclosed in copending U.S. patent application Ser. No 08/127,670, filed Sep. 28, 1993. In that application it is taught that an improved release agent reservoir and wick can be produced by wrapping an absorptive oil-filled material within a porous expanded polytetrafluoroethylene (PTFE) case. This device demonstrates superior oil transfer properties, providing an even distribution of oil over an extended period of time. The nature of this device allows it to function quite well in a variety of orientations and it is particularly suitable for use in portable machines or other applications that must withstand tilting or rapid movements. Moreover, the expanded PTFE case is particularly wear resistant and even can be rotated to further prolong its operating life.
While the device of the parent application is believed to be a significant improvement over previous release agent supply devices, further improvements are still believed desirable. For instance, the smooth surface of an expanded PTFE membrane casing does not remove excess toner and other particles as thoroughly as might be desired. Further, better control of the rate of supply of release agent is desired.
Accordingly, it is a primary purpose of the present invention to provide an apparatus for applying release chemicals to a roller which is durable, delivers a consistent coating of chemical to the roller, and provides effective cleaning of the roller.
It is a further purpose of the present invention to provide such an apparatus which has improved operational life by being readily adjusted to position multiple contact surfaces between apparatus and the roller.
It is yet another purpose of the present invention to provide an apparatus for applying release chemicals to a roller which is not prone to leakage and which can effectively operate at other than level orientations.
It is another purpose of the present invention to provide an apparatus that has improved cleaning properties, including improved ability to remove excess toner or other deposits from the roller.
It is still another purpose of the present invention to provide an apparatus for applying release chemicals to a roller which can be readily cleaned and reconditioned for reuse.
It is an additional purpose of the present invention to provide straightforward methods to produce and use an applicator with these properties. These and other purposes of the present invention will become evident from review of the following specification.